The field of the invention relates generally to advanced diagnostics in modular power converters, and more particularly, to current unbalance detection in modular power converters.
In at least some known power conversion systems, it is relatively common to increase the power rating of a converter by replicating (i.e., paralleling) a conversion circuit. One implementation of this technique is the straight paralleling of power semiconductors, as shown in FIG. 1. Specifically, a known power conversion system 10 includes, for each of three phases, three insulated gate bipolar transistor (IGBT) power converters 12 coupled in parallel. In such a configuration, all paralleled power converters 12 share the same pulse-width modulation (PWM) (i.e., they receive the same PWM control signals), and load sharing is assumed, given characteristics of power converters 12 and geometry of power conversion system 10.
Another option for paralleling a conversion circuit is paralleling of converter legs through separate transformer primary windings (or through separate inductors in transformer-less implementation), as shown in FIG. 2. Specifically, a known power conversion system 20 includes, for each of three phases (i.e., U, V, W), a pair of power converters 22 coupled in parallel. In this configuration, all parallel power converters 22 also share the same PWM modulation. Introducing an impedance between paralleled power converters 22 facilitates mitigating potential unbalance due to differences in semiconductor characteristics and/or geometry of system 20. However, in the implementations of systems 10 and 20, current sharing is assumed but is not actively monitored. Accordingly, a load unbalance condition may go undetected, which may lead to premature failure of over-stressed modules.
One alternative approach is the active control of load sharing, by sensing the current in each converter leg, as shown in FIGS. 3 and 4. FIG. 3 shows a known power conversion system 30 that includes a centralized controller 32 communicatively coupled to a plurality of power conversion modules 34. Centralized controller 32 monitors an output current of each power conversion module 34, as well as a voltage across a load 36, and controls operation of power conversion modules 34 accordingly. FIG. 4 shows a known power conversion system 40 that includes a plurality of power conversion modules 42 each including an associated control module 44. Each control module 44 monitors an output current of an associated power conversion module 42, as well as a voltage across a load 46, and controls operation of the associated power conversion modules 42 accordingly. However, such systems may require complex cabling in case of a centralized solution (i.e., system 30), or distributed intelligence in case of decentralized solutions (i.e., system 40).